A static random access memory (SRAM) is commonly used for data storage when the SRAM is supplied with power. To meet the demand in portable electronics and high speed computation, it is desirable to integrate more data storage cells including cross-coupled invertors into a single SRAM chip and to lower power consumption thereof, for example, by replacing conventional transistors with vertical transistors having smaller size and lower power consumption. However, challenges have been emerged from integrating vertical transistors into a SRAM chip in the semiconductor industry.